1. Field of the Invention
This invention relates in general to systems for communicating binary encoded information in parallel via multiple trinary transmission lines.
2. Prior Art
It is well known that the transfer of binary encoded information via transmission lines in parallel can achieve much higher transfer rates than serial transfers. Parallel transmission is done by grouping the binary information into sets of binary bits (e.g., bytes which have a bit width of eight binary bits), and transferring a full set at a time, the binary bits of the set being transmitted simultaneously, i.e. in parallel. Transfer of a set of binary bits in parallel conventionally requires one transmission line per bit. Thus nine transmission lines are conventionally required to transfer a byte along with a check bit (such as a parity bit) in parallel. If the data is transmitted differentially then each transmission line is a pair of signal lines and each binary bit transferred in parallel requires a separate signal line pair.
Also, a signal marking points or periods in time when the transmitted data is valid on the transmission lines must be transmitted immediately before, after or along with the data. This signal is commonly referred to as a "data clock." For serial transmission of binary data via a single transmission line, the data clock can be encoded with the data, such as by using a Manchester encoding scheme, or it can be sent along with the data via a second transmission line. But when binary data is sent via parallel transmission lines time skewing of data and other factors typically require that the data clock be sent via a separate transmission line, thus necessitating an additional transmission line.
According to the invention described herein, sets of binary encoded information are converted to a three-state, i.e. trinary, encoded form suitable for transmission via two, or multiples of two, trinary transmission lines. A trinary transmission line according to this invention is a signal path between a three-state driver and a three-state receiving circuit. As will be explained herein, converting the data from a binary to a trinary form leaves at least one trinary state not needed for data and which state therefore can be used as a data clock. The system of this invention transfers all the information contained in the original binary form but requires fewer transmission lines for transfer, and moreover provides a data clock without the need for a separate data clock transmission line. For example, three binary bits and a data clock conventionally transmitted in parallel via four binary transmission lines can be converted and transferred using only two trinary transmission lines. As another example, nine binary bits, representing a byte of information plus one check bit and a data clock can be transferred, including a data clock, using only six transmission lines. For a given clock rate, the data transfer rate is thereby increased because more information can be transferred per line per clock.
The invention can also be used to advantage to increase the transmission rate of data over present systems that use one or two wire-pairs to cover long distances. The transmission rate of a single or two wire-pair system is limited by the wire medium used and the distance between transmitter and receiver. A data transmission system according to this invention using the same wire medium and over the same distance can increase the data rate by a factor of nine (i.e. from 1,000,000 to 9,000,000 bits per second) when six wire-pairs are used. A system according to this invention is self-timing and can transmit 1.5 binary bits of worth of information per transmission line pair for each clock time, and the long distance transmission characteristics of differential signaling is maintained.
Other advantages and attributes of this invention will be discussed hereinafter and will be apparent upon a reading of the text hereinafter.